In case where an Ni-based superalloy is used as the substrate of a turbine blade or a turbine vane of a jet engine or a gas turbine or the like, the combustion gas temperature in early-stage jet engines was not so high, and therefore the turbine blade and the turbine vane were used with no cooling. However, in a gas turbine engine such as typically a recent jet engine, the inlet port gas temperature of the turbine is kept higher for the purpose of increasing the output power and the efficiency thereof. With that, the turbine blade or the turbine vane for a large-scale power generation gas turbine is so designed as to have a hollow structure for maintaining the high-temperature strength thereof, in which the inside of the blade or the vane is forcedly cooled with air or vapor to thereby prevent the increase in the temperature of the substrate. In such a turbine blade or a turbine vane, the blade or vane surface temperature is higher than 900° C. and, on the other hand, the inside of the blade or vane is at 600° C. or so. The temperature difference between the blade or vane surface and the inside thereof produced thermo-mechanical fatigue (TMF).
In particular, a turbine blade is exposed to high-temperature combustion gas and at the same time rotates at high speed, and therefore it must be resistant to high stress resulting from centrifugal force, and for this requirement, high-temperature creep characteristics are also important like TMF.
Heretofore, an Ni-based superalloy intended to have thermo-mechanical fatigue resistance is known (Patent References 1, 2). An Ni-based superalloy excellent in creep characteristics (Patent Reference 3) has many past results in practical use in a variety of high-temperature instruments.    Patent Reference 1: Japanese Patent 2841970    Patent Reference 2: Japanese Patent 3214330    Patent Reference 3: U.S. Pat. No. 4,643,782